Collapsible tire, method for collapsing same, and use thereof

ABSTRACT

The invention relates to a collapsible tyre for a vehicle, comprising at least one carcass reinforcement ( 5 ) surmounted radially from the outside by an inextensible crown reinforcement ( 4 ), itself radially on the inside of a tread ( 2 ), the said reinforcements ( 4, 5 ) each consisting of at least one layer of reinforcing elements, the said tread ( 2 ) being connected to two beads ( 6 ) by two sidewalls ( 8 ), the said beads ( 6 ) being intended to come into contact with a rim, each bead ( 6 ) comprising at least one circumferential reinforcing element ( 3 ) called a bead wire, the said bead wire ( 3 ) defining a mean line forming a substantially circular closed curve in a circumferential plane. 
     The bead wire ( 3 ) of each bead ( 6 ) is flexible and comprises at least one concave part P c  of smaller radius R c  and of centre of curvature C c . 
     The invention also relates to a method of collapsing the tyre and to a use of the tyre.

This application is a 371 of PCT/EP2012/062493, filed 27 June 2012, which claims benefit of FR1156414, filed 13 July 2011, the entire contents of each of which is incorporated by reference herein for all purposes.

BACKGROUND

1. Field

Disclosed herein is a collapsible radial or cross-ply tire, to a method of collapsing and to a use thereof on a passenger vehicle.

2. Description of Related Art

In what follows:

-   -   a “circumferential plane” means a plane perpendicular to the         axis of rotation of the tire,     -   an “eguatorial plane” means a circumferential plane passing         through the middle of the tread surface of the tire, and     -   a “radial plane” means a plane containing the axis of rotation         of the tire,     -   an “axial direction” means a direction parallel to the axis of         rotation of the tire,     -   a “radial direction” means a direction intersecting the axis of         rotation of the tire and perpendicular thereto,     -   a “circumferential direction” means a direction tangential to         the surface of the tread in the direction of rotation of the         tire,     -   “radially on the inside of” means closer to the axis of rotation         of the tire,     -   “radially on the outside of” means further from the axis of         rotation of the tire,     -   “axially on the inside of” means closer to the eguatorial plane,     -   “axially on the outside of” means further away from the         eguatorial plane.

A tire comprises a tread intended to come into contact with the ground via a tread surface, extending radially towards the inside in the form of two sidewalls connected to two beads intended to provide the connection between the tire and a rim.

A radial tire more particularly comprises a reinforcing structure comprising a crown reinforcement, radially on the inside of the tread, and a radial carcass reinforcement, radially on the inside of the crown reinforcement.

A cross ply tire differs from a tire built with radial tire technology in that there are at least two crossed carcass plies making angles other than 90° with respect to the circumferential direction of the tire. The plies are said to be “crossed” because the angles are of opposite sign from one ply to the other.

The carcass reinforcement usually comprises at least one pair of reinforcing elements which consists of threads substantially parallel to one another and usually making, with the circumferential direction, an angle comprised between 85° and 95°. The carcass reinforcement is, in most tires, and in each bead, wound from the inside towards the outside of the tire around a circumferential reinforcing element called a bead wire to form a turn-up. The bead wire may be formed of an assembly of elementary threads or of cords, themselves formed of an assembly of elementary threads.

The crown reinforcement generally comprises several crown reinforcement layers. These layers most often consist of metal reinforcing elements embedded in an elastomeric material.

In the case of a tire for a passenger vehicle, the thickness of the crown reinforcement, which essentially consists of the radial stack of the crown reinforcement and of the carcass reinforcement, is usually comprised between 2 and 7 mm. A sidewall of a tire for a passenger vehicle generally has a thickness comprised between 2.6 and 7 mm.

A collapsible tire for a bicycle, comprising a carcass reinforcement each end of which is anchored in two beads by being turned up around a reinforcing element called a bead wire is already known from document WO 10/100088. Each bead is extended radially by sidewalls which join to a tread. This tire comprises a bead wire formed by winding a saturated and unwrapped metal cord formed of filaments.

A collapsible tire mounted on a rim, for vehicles such as motor vehicles, is also known, from document FR 2 348 065. This tire comprises a substantially annular tread situated centrally, and sidewalls which extend the tread and end in inextensible beads, which means beads the bead wire of which has a high level of circumferential rigidity. When the tire is deflated, the sidewalls can be bent inwards towards one another so as to be practically flattened inside the tire in relation to the tread.

Finally, document U.S. Pat. No. 4,057,091 also discloses the collapsing of a tire for a motor vehicle when it is mounted on a rim. In such a combination and when deflated, the tire can be flattened by folding its sidewalls in on themselves towards this rim.

However, such tire collapsing configurations for motor vehicles assume the rim still to be present, and still occupy a great deal of space and exhibit a high weight due to the presence of the rim.

Moreover, when the tires are manufactured at production sites distant from the sales sites it is necessary to transport them. When they are being transported, even if compressed together, the tires still occupy a substantial volume.

Specifically, one mode of packaging currently employed is first of all to lay a first row of tires vertically and in a line to make an angle of inclination with the ground so that they are partially superposed. Other tires are then incorporated and pushed into that part of the hole of each tire of the first row that has been left free, thus forming a second row. Such a mode of packaging allows 30% more tires to be packed in per m³ by comparison with a layout in which the tires are placed side by side without deformation.

Hence, a need to be able to package one or more tires for a motor vehicle, not mounted on rims, in a more or less compact manner for the time they spend in transport and/or in storage, and without damaging their internal structure while at the same time allowing them to revert very quickly back to their initial shape when they are no longer collapsed still remains.

SUMMARY

One object of embodiments of the invention is therefore a collapsible tire for a vehicle, comprising at least one carcass reinforcement associated with an inextensible crown reinforcement, itself radially on the inside of a tread, the said reinforcements each consisting of at least one layer of reinforcing elements, the said tread being connected to two beads by two sidewalls, the said beads being intended to come into contact with a rim, each bead comprising at least one inextensible circumferential reinforcing element called a bead wire, the said bead wire defining, when free of any stress, a mean line forming a substantially circular closed curve in a circumferential plane, the said sidewalls having a thickness comprised between 2.6 and 7 mm and the said crown reinforcement having a thickness comprised between 2 and 7 mm. The invention is characterized in that the bead wire of each bead is flexible, and in that after the tire has been collapsed, the mean line of the bead wire comprises at least one concave part P_(c) of smaller radius R_(c) and of center of curvature C_(c).

The subject matter of embodiments of the invention covers both tires comprising a crown reinforcement radially on the inside of the carcass reinforcement and tires comprising a crown reinforcement radially on the outside of the carcass reinforcement.

A bead wire is said to be flexible when, flexed in its plane about a pulley of 10 mm radius, none of the rigid elements of which it is made suffers permanent deformation.

According to embodiments of the invention, a crown reinforcement is inextensible when the load to deform it by 5% is at least egual to 40 N, and a bead wire is inextensible when the load to lengthen it by 1% is at least equal to 2500 N.

The concave part is defined by a center of curvature on the outside of the closed mean line of the bead wire. The convex part is defined by a center of curvature on the inside of the closed mean line of the bead wire.

The tire according to embodiments of the invention has the advantage that the number of tires per unit volume for tire transport and/or storage can be increased significantly, leading to substantial economic savings.

Specifically, the form of collapse according to embodiments of the invention allows tires to be stored with a 50% per m³ improvement notably on the mode of packaging known as lacing, explained earlier. The tire according to the invention can be collapsed and stored loose or in a case.

Another advantage of embodiments of the tire of the invention is that it can be collapsed in various ways and kept collapsed in that way, regardless of its size. Finally, the tire according to the invention can remain collapsed for the time it spends in transport and/or storage without any negative impact on its performance.

Another subject of embodiments of the invention is a first method for collapsing a tire as defined previously, which consists in:

-   parting, in a radial plane, the beads of a part of the tire along an     axial direction towards an axis tangential to the center of the     tread of the said part of the tire in the said radial plane, -   applying a force in a radial direction to the said tread so as to     move it closer to the cavity opposite thus forming, in a     circumferential plane, a tire that is collapsed substantially into     the shape of an arc of a circle comprising a base that is connected     with two axes.

The parting step means increasing the axial distance between the beads.

Another subject of embodiments of the invention is a second method for collapsing a tire as defined hereinabove which consists:

-   in parting, in a radial plane, the beads of a first part of the tire     along an axial direction towards an axis tangential to the center of     the tread and in applying a compression force in the radial     direction to the said tread, it being possible for the said force to     be applied at the same time as the beads are being parted and/or     afterwards, -   in applying a first force F₁ in a first circumferential direction to     the said tread so as to move the corresponding cavity closer to     another part of the cavity of the tire, -   in parting, in a radial plane, the beads of a second part of the     tire in an axial direction towards an axis tangential to the center     of the tread, -   in applying, either simultaneously or not, the compression force in     the radial direction to the said first and/or second part, and a     second force F₂ in a second circumferential direction, of opposite     sense to the said first force F₁ to the said tread so as to move the     corresponding cavity closer to another part of the cavity of the     tire.

Finally, a final subject of embodiments of the invention is a use of the tire as defined hereinabove for a passenger vehicle.

The mean line of the bead wire further comprises at least two points of inflexion I₁, I₂ delimiting the concave part P_(c).

The mean line of the bead wire further comprises at least two convex parts P_(x1), P_(x2) having two smaller radii R_(x1), R_(x2) and two centers of curvature C_(x1), C_(x2). Preferably, straight lines D₁, D₂ respectively connecting the center of curvature C_(c1) of the concave part P_(c) to each of the centers of curvature C_(x1), C_(x2) of the convex parts form an angle α comprised between 30° and 125°.

The mean line of the bead wire of each bead is preferably formed by winding a metal cord, formed of filaments. The diameter of the cord is preferably less than 1.5 mm, and it is saturated and unwrapped. The diameter of the filaments is preferably less than 0.25 mm.

A cord is said to be “saturated” when it is impossible to add an additional filament between the filaments that form the said cord. It is said to be “unwrapped” when it has no additional filament wound in a helix on the external surface of the said cord. A wrapping filament is usually chosen to have a diameter less than that of the filaments of the cord and is wrapped at a short pitch and in a direction that is the opposite of or the same as the direction in which the threads that form the external surface of the cord are wound. The prime function of a wrap is to limit the buckling of the cord.

For preference also, the diameter of the threads or filaments that form the cord is less than 0.20 mm. Such filament diameters will further contribute to the flexibility of the cord and limit the load necessary to collapse the tire.

One advantageous embodiment of the invention makes provision for the tensile modulus of the cord to be greater than 150 GPa.

Advantageously also, the cord can be bent into a radius of curvature comprised between 2 and 5 mm without suffering any deformation that would render the tire unusable. For preference, it can be bent to a radius of curvature less than 3 mm without suffering deformation that would render the tire unusable.

According to one alternative form of the embodiment of the invention, the cord is a layered metal cord of [L+M] or [L+M+N] construction comprising a first layer C1 of L threads of diameter d₁ with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 of M threads of diameter d₂ wound together in a helix at a pitch p₂ with M ranging from 3 to 12, the said layer C2 possibly being surrounded by an external layer C3 of N threads of diameter d₃, wound together in a helix at a pitch p₃, with N ranging from 8 to 20 .

When L is equal to 1, the first layer forms a central core consisting of a metal thread of diameter d₁.

Advantageously, according to this alternative form of embodiment, the pitch p₂ and the pitch p₃ are identical.

Advantageously also according to this alternative form of embodiment, the cord is a 19.18 metal cord of formula 1+6+12, the layers being formed with the same direction of rotation and with identical pitches of 10 mm. Such a cord allows the formation of a bead wire by winding 3 to 16 turns. The number of turns required is dependent on the size of tire and its use.

According to a first alternative form, after the tire has been collapsed, the mean line of the bead wire comprises a concave part P_(c) of smaller radius R_(c1) and of center of curvature C_(c1). The bead wire also comprises two convex parts P_(x1), P_(x2), respectively of smaller radii R_(x1), R_(x2), and of centers of curvature C_(x1), C_(x2). The straight lines D₁, D₂ respectively connecting the center of curvature C_(c1) of the concave part P_(c) to each of the centers of curvature C_(x1), C_(x2) of the convex part P_(x) form an angle α comprised between 40 and 140°. The geometric shape of the collapsed tire in this first alternative form closely resembles a U-shape or a J-shape depending on whether the straight lines D₁ and D₂ are the same length or different lengths.

According to a second alternative form, for preference, after the tire has been collapsed, the mean line of the bead wire comprises a concave part P_(c) of smaller radius R_(c1) and of center of curvature C_(c1). The bead wire comprises two convex parts P_(x1), P_(x2), respectively of smaller radii R_(x1), R_(x2), and of centers of curvature C_(x1), C_(x2). The straight lines D₁, D₂ respectively connecting the center of curvature C_(c1) of the concave part P_(c) to each of the centers of curvature C_(x1), C_(x2) of the convex part P_(x) may form an angle α comprised between 30 and 55°, and are preferably of different lengths. The geometric shape of the collapsed tire according to this second alternative form of collapse closely resembles a spiral shape.

Finally, according to a last alternative form of the invention, after the tire has been collapsed, the mean line of the bead wire may comprise two concave parts P_(c1), P_(c2), respectively of smaller radii R_(c1), R_(c2) and of centers of curvature C_(c1), C_(c2). It also comprises two convex parts P_(x1), P_(x2), respectively of smaller radii R_(x1), R_(x2), and of centers of curvature C_(x1), C_(x2). The straight lines D₁, D₂ respectively connecting the center of curvature C_(c1) of a concave part to each of the centers of curvature C_(x1), C_(x2) of the convex parts P_(x1), P_(x2) preferably form an angle α comprised between 95° and 125°, and are not the same length. The geometric shape of the collapsed tire according to this last alternative form closely resembles an S shape.

For each of the alternative forms, the range of values for the angle α makes it possible both to guarantee that the tire, for certain sizes, runs no risk of any impairment when left collapsed for a lengthy period of time and also guarantees a significant gain in the amount of compacting.

Whatever the shape into which it is collapsed, the ratio D₁/D₂ is preferably greater than or equal to 1 and less than 1.90 assuming that D₁ is greater than D₂ in terms of absolute value. The upper limit on this ratio is dependent on the size of the tire.

When collapsed into a more or less U-shape or J-shape, the ratio D₁/D₂ may be comprised between 1 and 1.60.

When collapsed into more or less a spiral shape, the ratio D₁/D₂ may be comprised between 1.0 and 1.80, and preferably higher than 1.30.

When collapsed into more or less an S shape, the ratio D₁/D₂ may be comprised between 1.20 and 1.90 and is preferably higher than 1.35.

The tire according to the invention preferably, after collapse, occupies a volume less than 65% per m³ by comparison with the lacing mode of packaging.

The invention will now be illustrated with the aid of various detailed embodiments that follow and which do not in any way limit the subject matter of the invention.

BRIEF DESCRIPTION OF DRAWINGS

The various measurements that follow have been taken on tires, collapsed according to the invention, of different sizes.

FIG. 1 depicts a schematic view in section on a radial plane, of half a tire in the uncollapsed state,

FIG. 2 depicts a schematic view in cross section on a circumferential plane of the collapsed tire of the invention according to a first embodiment,

FIG. 3 depicts a schematic view in cross section on a circumferential plane of the collapsed tire of the invention according to a second embodiment,

FIG. 4 depicts a schematic view in cross section on a circumferential plane, of the collapsed tire according to the invention, according to a third embodiment,

FIGS. 5A and 5B depict a schematic three-dimensional view of the various steps of a first method of collapsing, and

FIGS. 6A and 6B depict a schematic three-dimensional view of the various steps of a second method of collapsing.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 depicts a passenger vehicle tire, of general reference 1, in the uncollapsed state, comprising a tread 2 extended radially inwards by two sidewalls 8 connected to two beads 6, the said beads comprising a bead wire 3 (reinforcing element) (not depicted).

FIG. 1 depicts a tread 2 radially furthest towards the outside. Radially on the inside of the said tread 2 there are, in succession, an inextensible crown reinforcement 4 and a carcass reinforcement 5.

The said crown 4 and carcass 5 reinforcements are each made up of at least one layer of reinforcing elements (not depicted). The tread 2 is connected to two beads 6 by two sidewalls 8. Each bead 6 comprises at least one bead wire 3. This bead wire 3, which defines a mean line forming a substantially circular closed curve in a circumferential plane is inextensible and flexible.

The bead wire is preferably made of steel, and takes the form of a saturated and unwrapped cord formed of filaments; the said filaments being of a diameter equal to 0.18 mm. The cord is a 19.18 metal cord of formula 1+6+12, the layers being formed with the same direction of rotation and with identical pitches equal to 10 mm. Such a cord can be used to form a bead wire by winding 3 to 16 turns. The number of turns required is dependent on the size of the tire and its use.

The mean thickness E_(F) of the sidewall of the tire according to the invention, measured at the point located in the middle, in the radial direction, between the high point of the bead wire and the low point of the tire on the eguatorial plane, is comprised between 2.6 and 7 mm.

The mean thickness E_(S) of the crown reinforcement 4, measured in the eguatorial plane, is comprised between 2 and 7 mm.

In FIG. 2, the mean line of the bead wire 3 (depicted in dotted line) of the tire, of trade reference 185/65 R 14, collapsed according to a first mode of collapse, roughly into a U shape, has a concave part P_(c1) of smaller radius R_(c1) equal to 69 mm and a center of curvature C_(c1).

The mean line of the bead wire 3 comprises, on the one hand, two points of inflexion I₁, I₂ which delimit the concave part P_(c1) and, on the other hand, two convex parts P_(x1), P_(x2) having two smaller radii R_(x1) equal to 18 mm and R_(x2) equal to 18 mm and two centers of curvature C_(x1) and C_(x2).

Two straight lines D₁ and D₂ which respectively connect the center of curvature C_(c1) and concave part P_(c1) to each of the centers of curvature C_(x1) and C_(x2) of the convex part P_(x1) form an angle a of around 52°. In this mode of collapse the straight lines D₁ and D₂ are substantially the same length, and measure 170 mm.

In another alternative form of this same mode of collapse according to FIG. 2 of the tire of the same reference as previously, the two straight lines D₁ and D₂ which respectively connect the center of curvature C_(c1) of the concave part P_(c1) to each of the centers of curvature C_(x1), C_(x2) of the convex part P_(x1), have different lengths. D₁ is equal to 197 mm, D₂ is equal to 135 mm; the ratio D₁/D₂ is equal to 1.45 and the angle α is equal to 65°.

Having been collapsed according to this first mode of collapse, the tires can also be nested in one another or even possibly laced. Lacing makes it possible to keep them compressed.

Table I below collates other measurements taken on the form of collapse depicted in FIG. 2.

TABLE I Sidewall Crown thickness reinforcement Angle D₁ D₂ R_(c1) R_(x1) R_(x2) Size of (in mm) thickness α (in (in (in (in (in (in tire E_(F) (in mm) E_(S) degrees) mm) mm) mm) mm) mm) D₁/D₂ 175/70 3.7 3.2 51 138 138 77 16 16 1 R 13 185/65 4.5 2.7 61 170 170 68 18 18 1 R 14 185/65 4.5 2.7 65 197 135 69 17 17 1.45 R 14 195/65 4.8 3.7 124 156 156 111 30 30 1 R 15 205/55 5 3.7 55 168 168 78 18 18 1 R 16 225/55 5 3.2 45 189 189 96 16 16 1 R 17

The collapsing of the tire 1 as depicted in FIG. 3 differs from that of FIG. 2 in that the straight lines D₁ and D₂ form an angle α comprised between 38° and 57°, and in that they do not have the same length. The collapsing as depicted in FIG. 4 closely resembles the shape of a spiral.

The volume occupied by the tire is less than 85%, preferably less than 75% of the volume occupied by tires collapsed according to the currently known modes of packaging.

Table II below collates the measurements taken on various tires according to the form of collapse depicted in FIG. 3.

TABLE II Sidewall Crown thickness reinforcement Angle D₁ D₂ R_(c1) R_(x1) R_(x2) Size of (in mm) thickness α (in (in (in (in (in (in tire E_(F) (in mm) E_(S) degrees) mm) mm) mm) mm) mm) D₁/D₂ 175/70 3.7 3.2 42 125 83 29 19 19 1.50 R 13 185/65 4.5 2.7 38 135 83 25 15 15 1.63 R 14 195/65 4.5 2.7 42 136 93 26 16 16 1.46 R 15 205/55 4.8 3.7 37 154 94 27 17 17 1.64 R 16 225/55 5 3.7 46 149 110 24 14 14 1.35 R 17

The third mode of collapsing the tire 1, as depicted in FIG. 4, differs from that of FIG. 2 in that the mean line of the bead wire 3 comprises two concave parts P_(c1), P_(c2). The concave parts P_(c1) and P_(c2) are characterized by a smaller radius.

The mean line of the bead wire 3 also comprises two convex parts P_(x1), P_(x2) respectively having a smaller radius R_(x1) equal to 11 mm, and R_(x2) equal to 11 mm, and respectively having a center of curvature C_(x1), C_(x2).

In FIG. 4, the mean line of the bead wire 3 comprises three points of inflexion I₁, I₂ and I₃ which delimit a concave part from a convex part and vice versa.

According to this third mode of collapse, the straight lines D₁ and D₂ which respectively connect the center of curvature C_(c1) of a concave part P_(c1) to each of the centers of curvature C_(x1), C_(x2) of the convex parts P_(x1) and P_(x2) form an angle a comprised between 95° and 125°. The straight lines D₁ and D₂ are not of the same length.

The volume occupied by the tire is less than 80%, preferably less than 70% by comparison with the volume occupied by tires collapsed according to currently known modes of compacting.

Table III below collates the measurements taken on various tires according to the form of collapse depicted in FIG. 4.

TABLE III Sidewall Crown thickness reinforcement Angle D₁ D₂ R_(c1) R_(x1) R_(x2) Size of (in mm) thickness α (in (in (in (in (in (in tire E_(F) (in mm) E_(S) degrees) mm) mm) mm) mm) mm) D₁/D₂ 175/70 3.7 3.2 112 122 92 20 10 10 1.33 R 13 185/65 4.5 2.7 111 132 96 21 11 11 1.37 R 14 195/65 4.5 2.7 112 136 103 25 15 15 1.32 R 15 205/55 4.8 3.7 106 159 89 22 12 12 1.78 R 16 225/55 5 3.7 112 153 112 22 12 12 1.36 R 17

In order to obtain a collapsed tire according to the invention, there are two conceivable methods of collapsing.

The first method of collapsing results in the collapsed tire according to the invention indicated schematically in FIGS. 2 and 3. This method is indicated schematically in FIGS. 5A and 5B. As FIG. 5A shows, this method consists, in a radial plane, in parting the beads 6 towards an axis tangential to the center 2 a of the tread 2 in the said radial plane.

FIG. 5B shows that, in a radial direction, a force is applied to the said tread 2 either at the same time as the parting step and/or afterwards, so as to move this tread closer to the cavity 9 opposite. This then yields, in a circumferential plane, a tire that is collapsed substantially into the shape of semicircle and closely resembles a U shape. This shape in the form of an arc of a circle comprises two substantially vertical axes 10 a and 10 b which, when bent over on one another indiscriminately, yield the collapsed configuration of FIG. 3 which closely resembles a spiral.

The second method of collapsing the tire results in the collapsed tire according to the invention indicated schematically in FIG. 4.

This method is indicated schematically by FIGS. 6A and 6B. According to this second method of collapse, and as shown by FIG. 6A, the beads 6 of a first part 11 of the tire are, in a radial plane, parted in an axial direction towards an axis tangential to the center 2 a of the tread 2.

A compression force is applied in a radial direction to said tread 2 of the first part 11. The said force may be applied at the same time as the beads 6 are being parted and/or afterwards.

As FIG. 6B shows, a first compression force F₁ is applied, simultaneously or otherwise, in a first circumferential direction XX^(1′) to the tread 2 in order to move it closer to the cavity 13 opposite.

A second force F₂ is applied in a second circumferential direction parallel to the first force F₁, so as to move it closer to the cavity 14. The forces F₁ and F₂ are of opposite sense.

The compression force applied in the radial direction may be applied simultaneously with the second force F₂ or non-simultaneously therewith.

The tire collapsed according to this mode of collapse is more or less S-shaped. 

1. A collapsible tire for a vehicle, comprising at least one carcass reinforcement associated with an inextensible crown reinforcement, itself disposed radially on the inside of a tread, the reinforcements each comprising at least one layer of reinforcing elements, the tread being connected to two beads by two sidewalls, the beads being intended to come into contact with a rim, each bead comprising at least one inextensible circumferential reinforcing element called a bead wire, the bead wire defining, when free of any stress, a mean line forming a substantially circular closed curve in a circumferential plane, the sidewalls having a thickness between 2.6 and 7 mm and the crown reinforcement having a thickness between 2 and 7 mm, wherein the bead wire of each bead is flexible, wherein after the tire has been collapsed, the mean line of the bead wire comprises at least one concave part P_(c) of smaller radius R_(c) and of center of curvature C_(c).
 2. The tire according to claim 1, wherein the mean line of the bead wire further comprises at least two points of inflexion I₁, I₂ delimiting the concave part P_(c).
 3. The tire according to claim 1, wherein the mean line of the bead wire further comprises at least two convex parts P_(x1), P_(x2) having two smaller radii R_(x1), R_(x2) and two centers of curvature C_(x1), C_(x2), and wherein straight lines D₁, D₂ respectively connecting the center of curvature C₁ of the concave part P_(c) to each of the centers of curvature C_(x1), C_(x2) of the convex parts P_(x1), P_(x2) form an angle α between 30° and 125°.
 4. The tire according to claim 1, wherein the mean line of the bead wire of each bead is formed by winding a metal cord, formed of filaments, which is saturated and unwrapped, wherein the diameter of the cord is less than 1.5 mm and wherein the diameter of the filament is less than 0.25 mm.
 5. The tire according to claim 1, wherein after it has been collapsed, the mean line of the bead wire comprises a concave part P_(c) of smaller radius R_(c1)and of center of curvature C_(c1), wherein it comprises two convex parts P_(x1), P_(x2), respectively of smaller radii R_(x1), R_(x2), and of centers of curvature C_(x1), C_(x2), and wherein the straight lines D₁, D₂ respectively connecting the center of curvature C_(c1) of the concave part P_(c) to each of the centers of curvature C_(x1), C_(x2) of the convex part P_(x) form an angle α between 40 and 140°.
 6. The tire according to claim 1, wherein after it has been collapsed, the mean line of the bead wire comprises a concave part P_(c) of smaller radius R_(c1) and of center of curvature C_(c1), wherein it comprises two convex parts P_(x1), P_(x2) respectively of smaller radii R_(x1), R_(x2), and of centers of curvature C_(x1), C_(x2), and wherein the straight lines D₁, D₂ respectively connecting the center of curvature C_(c) of the concave part P_(c) to each of the centers of curvature C_(x1), C_(x2) of the convex part P_(x) form an angle α comprised between 30 and 55°.
 7. The tire according to claim 1, wherein after it has been collapsed, the mean line of the bead wire comprises two concave parts P_(c1), P_(c2), respectively of smaller radii R_(c1), R_(c2) and of centers of curvature C_(c1), C_(c2), wherein it comprises two convex parts P_(x1), P_(x2), respectively of smaller radii R_(x1), R_(x2), and of centers of curvature C_(x1), C_(x2), wherein the straight lines D₁, D₂ respectively connecting the center of curvature C_(c1) of a concave part to each of the centers of curvature C_(x1), C_(x2) of the convex parts P_(x1), P_(x2) form an angle α between 95° and 125°.
 8. The tire according to claim 7, wherein after collapsing, ratio D₁/D₂ is greater than or equal to 1 and less than 1.9.
 9. The tire according to claim 1, wherein after collapsing, it occupies a volume less than 65% per m³ by comparison with a lacing mode of packaging.
 10. A method for collapsing a tire according to claim 1, comprising: parting, in a radial plane, the beads of a part of the tire along an axial direction towards an axis tangential to the center of the tread of the said part of the tire in the said radial plane, applying a force in a radial direction to the said tread so as to move it closer to a cavity opposite thus forming, in a circumferential plane, a tire that is collapsed substantially into the shape of an arc of a circle comprising a base that is connected with two axes.
 11. The method according to claim 10, further comprising, in the circumferential plane, folding the two axes one onto the other indiscriminately.
 12. A method for collapsing a tire according to claim 1, comprising: parting, in a radial plane, the beads of a first part of the tire along an axial direction towards an axis tangential to the center of the tread and in applying a compression force in the radial direction to the said tread, it being possible for the force to be applied at the same time as the beads are being parted and/or afterwards, applying a first force F1 in a first circumferential direction to the said tread so as to move a corresponding cavity closer to another part of the cavity of the tire, parting, in a radial plane, the beads of a second part of the tire in an axial direction towards an axis tangential to the center of the tread, applying, either simultaneously or not, a compression force in the radial direction to the said first and/or second part, and a second force F2 in a second circumferential direction, of opposite sense to the said first force F1 to the said tread so as to move the corresponding cavity closer to another part of the cavity of the tire.
 13. A method of the tire according to claim 1 comprising installing the tire on a passenger vehicle. 